The present invention relates to methods, apparatuses, units and computer programs for processing images, notably for combining overlapping images of an area of interest. The invention may, for instance, be used in geographical information systems for urban planning, scientific investigation or environmental impact assessment.
In geographical information systems, it is often desirable to construct an image of an area of interest, for instance an aerial photograph, by combining a plurality of overlapping images obtained from different points, i.e., locations.
The image construction process generally first includes a geometric rectification of the images, such as a perspective correction. The perspective correction may also be carried out during exposure by an adapted correction lens. The rectification process produces orthorectified images. The images may also be subject to scaling, lens distortion correction, color or brightness correction, and the like.
The construction process then generally includes making the images correspond to an available digital terrain model (DTM), digital surface model (DSM) or digital elevation model (DEM), i.e., a digital representation of ground surface topography. A digital terrain model (DTM) is obtained by remote sensing or land surveying, for instance.
The image construction process finally includes combining the overlapping images, by alignment and superposition for instance.
Conventional methods for combining overlapping images from different locations may require additional processing to obtain a smooth combined image, i.e., a combined image with an unnoticeable transition between the original constituent images. This may be needed to cope with specific characteristics of the area of interest. This additional processing is often laborious and inefficient.
It is therefore desirable to provide an image processing method which solves or partially solves the above-mentioned problems. In particular, there is a need for providing a process for combining overlapping images of an area of interest which produces smoother combined images and which can be performed in an automatic manner, such as on a computer.